The primary aim of the proposed research is to advance our knowledge about the development of the psychological processes involved in scientific discovery. The research program is guided by a detailed model of the components of the scientific discovery process. This model characterizes scientific discovery as a problem-process involving search in several problem spaces including the space of hypotheses and the space of experiments. The aim is to identify the developmental trajectory of the processes that execute, constrain and integrate the search. The empirical work includes several studies of how people generate experiments, form and revise hypotheses, evaluate evidence, and collaborate on complex reasoning tasks. Participants include preschoolers, elementary school children, and both science and non- science college students. The theoretical work will elaborate and refine the dual search framework. The research proposed in the current application will have a specific emphasis on the development of evidence evaluation processes. Four interrelated projects are proposed: . Studies of young children's understanding of indeterminacy. This is a fundamental aspect of scientific reasoning. Although preschoolers have a good understanding of the distinction between certain types of determinate and indeterminate patters of evidence, there are others that are extremely resistant to change. The proposed studies will investigate will investigate the nature of this problem. . Studies of elementary school children's learning and transfer of strategies for designing unconfounded experiments. We will explore questions raised in earlier in earlier studies about individual differences in the acquisition and transfer of a basic experimental skill. . Investigation of an important aspect of collaboration in science: the decision to engage or disengage from a collaboration, during the problem solving session. Collaboration is an effective aspect of scientific discovery and although collaborative problem solving has been extensively studied, little is known about the cognitive factors that determine why people decided to work together or apart during their problem solving efforts. Moreover, collaboration requires explicit articulation of one's evidential basis for an argument or belief and may thereby affect the evidence evaluation process. . Revision and extension of our current model of the discovery process. The extended framework will have additional problem spaces that will be used to organized, interpret and integrate the results of these studies.